Medical devices to simultaneously cut and staple tissue in a surgical patient, often called linear cutters, are commonly used in endoscopic surgery. In endoscopic surgery, linear cutters are placed into the patient through a cannula having a small orifice. Each linear cutter generally has an end-effector in the form of a cartridge, for holding and ejecting staples, and an anvil, for forming the ejected staple into the proper shape. After passing through the cannula, the cartridge and anvil are clamped around tissue to be cut and stapled to compress the tissue and stem blood flow. The tissue exerts a reactive force against the cartridge and the anvil of the device. Examples of linear cutters can be found in U.S. Pat. Nos. 6,032,849 and 5,673,840, both of which are hereby incorporated herein by reference.
An anvil of a linear cutter has depressions positioned within it. Each depression receives the legs of a “C” shaped staple ejected towards it and bends the legs of the staples to form “B” shaped closures. To keep each pocket positioned in the correct position and at the correct distance from the cartridge, it is advantageous to minimize anvil deflection. Force exerted against the anvil from the tissue causes bending of the anvil and channel of the end-effector in a plane orthogonal to the tissue surface. The bending displaces the staple-forming portion of the anvil from the optimum position to receive an ejected staple, and may result in malformation of staples. The malformation has a greater potential for occurring when the cartridge and the anvil of the device are made longer.
A technique for creating a stiffer anvil is to increase the dimension of the anvil in the plane of bending. This dimension is commonly called the height of the anvil, and increasing the height of the anvil can also enlarge the cross-sectional area of the anvil. However, the benefits of endoscopic surgery stem from creating small incisions on the patient. Small incisions use small cannulas, and a small cross-sectional area for the anvil is desirable to fit the jaws of the device through a small cannula. Longer working jaws are desirable, but jaw length has been limited by the need to maintain small cross-sectional area and efficacious staple formation. Deflection needs consideration not only in the design of endoscopic linear cutters, but also in any endoscopic device having an attached implement that receives a reactive force from tissue or the work being performed.
Because of the benefits of a small incision, there has been a desire to use an implement that will have a short height to facilitate entry through a small orifice and that will expand to a greater height to become more rigid while being used inside the body. The present invention provides for a surgical device having a working implement with a movable device that can be raised to increase the implement rigidity, and that can be lowered to decrease implement height to facilitate insertion through a cannula.